refactor: use Stroke protocol annotation in place of PenStroke

Memola/Canvas/Contexts/GraphicContext.swift

@@ -11,11 +11,12 @@ import CoreData
 import Foundation
 
 final class GraphicContext: @unchecked Sendable {
-    var strokes: [PenStroke] = []
+    var strokes: [any Stroke] = []
     var object: GraphicContextObject?
+    
+    var currentStroke: (any Stroke)?
+    var previousStroke: (any Stroke)?
 
-    var currentStroke: PenStroke?
-    var previousStroke: PenStroke?
     var currentPoint: CGPoint?
     var renderType: RenderType = .finished
     var vertices: [ViewPortVertex] = []
@@ -40,7 +41,7 @@ final class GraphicContext: @unchecked Sendable {
         guard !strokes.isEmpty else { return }
         let stroke = strokes.removeLast()
         withPersistence(\.backgroundContext) { [stroke] context in
-            stroke.object?.graphicContext = nil
+            stroke.stroke(as: PenStroke.self)?.object?.graphicContext = nil
             try context.saveIfNeeded()
         }
         previousStroke = nil
@@ -51,7 +52,7 @@ final class GraphicContext: @unchecked Sendable {
         case .stroke(let stroke):
             strokes.append(stroke)
             withPersistence(\.backgroundContext) { [weak self, stroke] context in
-                stroke.object?.graphicContext = self?.object
+                stroke.stroke(as: PenStroke.self)?.object?.graphicContext = self?.object
                 try context.saveIfNeeded()
             }
             previousStroke = nil
@@ -92,7 +93,7 @@ extension GraphicContext {
     func loadQuads(_ bounds: CGRect) {
         for stroke in self.strokes {
             guard stroke.isVisible(in: bounds), stroke.isEmpty else { continue }
-            stroke.loadQuads()
+            stroke.stroke(as: PenStroke.self)?.loadQuads()
         }
     }
 }
@@ -114,7 +115,7 @@ extension GraphicContext: Drawable {
 }
 
 extension GraphicContext {
-    func beginStroke(at point: CGPoint, pen: Pen) -> PenStroke {
+    func beginStroke(at point: CGPoint, pen: Pen) -> any Stroke {
         let stroke = PenStroke(
             bounds: [point.x - pen.thickness, point.y - pen.thickness, point.x + pen.thickness, point.y + pen.thickness],
             color: pen.rgba,
@@ -156,7 +157,7 @@ extension GraphicContext {
         currentStroke.saveQuads(to: currentStroke.quads.endIndex)
         withPersistence(\.backgroundContext) { context in
             try context.saveIfNeeded()
-            if let stroke = currentStroke.object {
+            if let stroke = currentStroke.stroke(as: PenStroke.self)?.object {
                 context.refresh(stroke, mergeChanges: false)
             }
         }
@@ -169,7 +170,7 @@ extension GraphicContext {
         if !strokes.isEmpty {
             let stroke = strokes.removeLast()
             withPersistence(\.backgroundContext) { [graphicContext = object, _stroke = stroke] context in
-                if let stroke = _stroke.object {
+                if let stroke = _stroke.stroke(as: PenStroke.self)?.object {
                     graphicContext?.strokes.remove(stroke)
                     context.delete(stroke)
                 }

Memola/Canvas/Core/Canvas.swift

@@ -104,7 +104,7 @@ extension Canvas {
 
 // MARK: - Graphic Context
 extension Canvas {
-    func beginTouch(at point: CGPoint, pen: Pen) -> PenStroke {
+    func beginTouch(at point: CGPoint, pen: Pen) -> any Stroke {
         graphicContext.beginStroke(at: point, pen: pen)
     }
 
@@ -124,7 +124,7 @@ extension Canvas {
         graphicContext.renderType = renderType
     }
 
-    func getNewlyAddedStroke() -> PenStroke? {
+    func getNewlyAddedStroke() -> (any Stroke)? {
         graphicContext.strokes.last
     }
 }

Memola/Canvas/Geometries/Stroke/Core/Stroke.swift

@@ -117,3 +117,9 @@ extension Stroke {
         hasher.combine(id)
     }
 }
+
+extension Stroke {
+    func stroke<S: Stroke>(as type: S.Type) -> S? {
+        self as? S
+    }
+}

Memola/Canvas/History/History.swift

@@ -53,7 +53,7 @@ class History: ObservableObject {
             switch event {
             case .stroke(let _stroke):
                 withPersistence(\.backgroundContext) { context in
-                    if let stroke = _stroke.object {
+                    if let stroke = _stroke.stroke(as: PenStroke.self)?.object {
                         context.delete(stroke)
                     }
                     try context.saveIfNeeded()

Memola/Canvas/History/HistoryEvent.swift

@@ -8,5 +8,5 @@
 import Foundation
 
 enum HistoryEvent {
-    case stroke(PenStroke)
+    case stroke(any Stroke)
 }

Memola/Canvas/RenderPasses/EraserRenderPass.swift

@@ -16,7 +16,7 @@ class EraserRenderPass: RenderPass {
     var eraserPipelineState: MTLRenderPipelineState?
     var quadPipelineState: MTLComputePipelineState?
 
-    var stroke: PenStroke?
+    var stroke: (any Stroke)?
     weak var graphicTexture: MTLTexture?
 
     init(renderer: Renderer) {

Memola/Canvas/RenderPasses/StrokeRenderPass.swift

@@ -18,7 +18,7 @@ class StrokeRenderPass: RenderPass {
     var quadPipelineState: MTLComputePipelineState?
     weak var graphicPipelineState: MTLRenderPipelineState?
 
-    var stroke: PenStroke?
+    var stroke: (any Stroke)?
     var strokeTexture: MTLTexture?
 
     init(renderer: Renderer) {